Participation in long-distance running events, such as marathons and half-marathons, has increased over recent years. Cardiac arrest among participants, although uncommon, is widely publicized when it occurs. However, the absolute risk of cardiac arrest during running events and the epidemiology surrounding it has been relatively unstudied. The goal of this paper was to assess the incidence and outcomes of cardiac arrest associated with marathon and half-marathon races in the United States over a 10-year period. By analyzing medical records as well as interviewing survivors and the next of kin of nonsurvivors, the authors were able to make conclusions about the causes and risk factors for running-related cardiac arrests (e.g., age, sex, number of previous races run). By using publicly available race participant statistics, the authors estimated that 10.9 million runners participated in marathon and half-marathon races in the US over the 10-year time period. There were 59 cases of cardiac arrest identified by using public search engines to search for running-related deaths which were then verified with additional searches of relevant websites or contact with race officials. The mean age of runners with cardiac arrest was 42 ± 13 years and 86% were men. The overall incidence of cardiac arrest was 1 per 184,000 participants and was significantly higher during marathons (1.01 per 100,000) than during half-marathons (0.27 per 100,000). Medical records from 31 runners were available for further review, which demonstrated that the strongest predictors of survival of cardiac arrest were initiation of bystander-administered cardiopulmonary resuscitation (CPR) and an underlying diagnosis other than hypertrophic cardiomyopathy. The authors also showed that survivors were more likely to be older than nonsurvivors (53.1 ± 6.5 vs. 33.9 ± 9.5 years).

This study has several important conclusions. First of all, it shows that cardiac arrest during long-distance running races is uncommon; however, for a certain population (older male runners participating in full marathons) the risk is greater. At first, it may seem surprising that survivors of cardiac arrest during running events tended to be older than nonsurvivors; however, the cause of cardiac arrest in a younger runner is more likely to be related to hypertrophic cardiomyopathy; which is more difficult to resuscitate versus heart disease due to atherosclerosis. The study also shows that male runners are clearly at higher risk, which is likely due to a higher prevalence heart disease in men. The incidence of cardiac arrest and death were also 3 to 5 times higher for marathon versus half-marathon runners showing an effect of prolonged physical effort. Although previous authors have suggested that exercise-induced cardiac events result from coronary plaque disruption and thrombus formation, this study found little evidence of this when examining autopsy results from nonsurvivors and coronary angiography from survivors. These authors suggest that increased oxygen demand from the stress of distance running may cause ischemia in individuals with previously undetected coronary stenosis. Whether or not this high-risk subpopulation of participants (middle-aged and older men) should be screened with in-office exercise stress testing is debatable due to cost and high rates of false positive results. However, a careful screening for symptoms during training seems easily feasible and could help determine who should have further testing. Another important point that this paper makes is that the overall case fatality rate for these long-distance races was better than that for out-of-hospital cardiac arrests (71% vs. 92%). For those of us who are involved with providing medical coverage for these mass participation events, this is encouraging data. Do you screen your recreational endurance athletes for exercise-induced coronary symptoms? And do you ever advise against long-distance running program for high-risk individuals?

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comments:

Anonymous
said...

I would like to see more research on this subject. Seeing more and more men in their early to mid 30's succumbing to this. Has anyone looked at Heat, dehydration, electrolytes, etc. as a factor? How about when swimming? Seems like this is becoming an issue with Triathlons, especially during the swim. And how can a person run multiple races, even strong marathons, and then all of sudden drop dead?? Just questions that very few if anyone has researched.

Agreed that more research on this topic is needed. Cardiac death in athletes likely represents a number of different etiologies which is difficult to study because it has to be done retrospectively and with some amount of speculation. Although training my be somewhat protective from heart disease in general, it is by no means a safeguard from cardiac death.

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